Process for preparing a polysiloxane

ABSTRACT

A novel process is disclosed for the preparation of a polysiloxane that is useful in the preparation of an emulsion for rendering flexible sheet material non-adherent to surfaces which normally adhere thereto.

This invention relates to a novel procedure for the preparation of apolysiloxane that is useful in the preparation of an emulsion forrendering flexible sheet material non-adherent to surfaces which wouldordinarily adhere thereto.

BACKGROUND OF THE INVENTION

Polysiloxane based emulsions have been employed in the prior art forrendering flexible sheet materials non-adherent to surfaces that wouldordinarily adhere thereto. These products have normally consisted of asilanol chain-stopped di-substituted polysiloxane which is cross-linkedwith a hydrogen containing polysiloxane. This reaction has beencatalyzed by an organotin salt of a fatty acid.

In copending application Ser. No. 419,372, filed Nov. 27, 1973 and nowU.S. Pat. No. 3,900,617 the limitations of the above-noted systems havebeen mentioned. That application is hereby incorporated by reference.

It has now been discovered that a greatly improved product for renderingflexible sheet material non-adherent to surfaces that would ordinarilyadhere thereto will be obtained from a vinyl containing polysiloxanebased emulsion, if the vinyl containing polysiloxane is prepared using adifferent procedure. The novel process provides an emulsion product thatoffers the following advantages:

A. Lower manufacturing costs;

B. Improved shear, dilution and freeze-thaw stability;

C. Less penetration into porous substrates;

D. More resistance to inhibition of cure on selected substrates;

E. More resistance to rub-off from certain substrates.

The above-described advantages are secured by preparing a polysiloxanehaving a vinyl unsaturation by a process which is based on firsthomogenizing the tetramer reactants in water in the presence of asubstituted benzene sulfonic acid, heating the tetramer reactants topolymerize the polysiloxane and adding an alkanolamine to terminate thepolymerization reaction. A platinum catalyst may be dispersed with thetetramers prior to polymerization without risk of poisoning ordeactivation. Alternatively, the platinum catalyst may be dispersed intothe finished emulsion after addition of the alkanolamine, or at anysubsequent time prior to the preparation of the coating bath.

DETAILED DESCRIPTION OF THE INVENTION

The invention is primarily directed to process for preparing an emulsionof a polysiloxane having the formula: ##STR1## wherein R is a monovalenthydrocarbon radical free of unsaturation; R¹ is a hydrocarbon radicalhaving vinyl unsaturation; x and y are positive integers so that thepolysiloxane has from 0.1 to 1.0% by weight of R¹ groups and theviscosity of the polymer ranges between 25,000 centipoises and 1,000,000centipoises. The process comprises:

a. homogenizing a mixture of:

i. a compound of the formula (R₂ SiO)₄ wherein R is a monovalenthydrocarbon free of unsaturation;

ii. a compound of the formula (RR¹ SiO)₄ wherein R is the same ashereinabove defined and R¹ is a hydrocarbon radical having vinylunsaturation;

iii. a benzene sulfonic acid compound of the formula: ##STR2## whereinR² is an alkyl group of from 6--18 carbon atoms; and iv. a platinumcatalyst if desired;

b. heating the homogenized mixture of (a) to polymerize thepolysiloxane; and

c. adding a neutralizing amount of an alkanolamine to said mixture toneutralize said benzene sulfonic acid compound.

The preferred polysiloxanes are of the formulae: ##STR3## wherein x andy are the same as hereinabove defined.

The R groups of Formula 1 are monovalent hydrocarbon groups free ofvinyl unsaturation and may be alkyl, e.g., methyl, ethyl, propyl, butyl,octyl, etc., aryl, e.g., phenyl, tolyl, xylyl, etc., cycloalkyl, e.g.,cyclohexyl, cycloheptyl, etc., aralkyl, e.g., benzyl, phenethyl, etc.,halogenated aryl, e.g., chlorophenyl, bromophenyl, chloronaphthyl, etc.,cyanoalkyl, e.g., cyanoethyl, cyanopropyl, etc., or mixtures of any ofthe foregoing. R¹ is preferably vinyl but may also be (CH₂)_(n) --CH=CH₂wherein n is an integer of from 1 to 10.

A platinum catalyst, for cross-linking the above-described polysiloxanewith an organohydrogenpolysiloxane may be added prior to initiation ofthe tetramer polymerization or after as discussed hereinabove.

The polymerization reaction is carried out by heating the reactionmixture at a temperature of from 40°-100° C., and more preferably, at atemperature of from 60°-80° C.

The heating cycle is followed by a cooling cycle during whichsignificant increases in the molecular weight of the polysiloxane occur.The cooling cycle is induced by withdrawal of the heat source andthereafter the reaction is allowed to cool to ambient temperature. Inthe alternative, associated cooling means such as refrigeration coilsmay be employed. The heating cycle will usually comprise a period offrom 1 to 24 hours, preferably, 2 to 4 hours and the cooling cycle willusually comprise from 1 to 8 hours, preferably, 2 to 5 hours. At the endof the cooling cycle, the alkanolamine is added to the reaction mixtureto neutralize the benzene sulfonic acid. The alkanolamine is selectedfrom compounds of the formula:

    (R.sup.3 OH).sub.3 N                                       (V)

wherein R³ is lower alkylene of from 1 to 8 carbon atoms such asmethylene, ethylene, propylene, butylene, octylene, etc. The preferredalkanolamine is triethanolamine. The amount of alkanolamine is based onthe amount of benzene sulfonic acid and is sufficient to neutralize thisacid. The alkanolamine is added with agitation to terminate the coolingcycle.

It is believed that during the heating step, the benzene sulfonic acidis actually acting as an equilibration catalyst. However, at lowertemperatures, the polymerization process is kinetically favored comparedto any "cracking" process. It has been observed that the longer thecooling cycle, the higher will be the molecular weight of thepolysiloxane as measured by the viscosity.

If desired, conventional techniques may be used to break thepolysiloxane emulsion. For example, a lower alkanol may be added tobreak the emulsion. The lower alkanol may be methanol, ethanol,propanol, etc.

The polysiloxanes of Formula (I) and (II) are useful in a process forrendering flexible sheet material non-adherent to surfaces whichnormally adhere thereto which process comprises:

a. treating the sheet material with aqueous emulsions containing:

i. the polysiloxane containing vinyl unsaturation that is produced bythe above-described process;

ii. an organic hydrogen polysiloxane having the formula:

    (R).sub.a (H).sub.b SiO.sub.4-a-b/2                        (VI)

wherein R is a monovalent hydrocarbon radical free of unsaturation, a isfrom 0 to 3, and the sum of a plus b is from about 0.8 to 3, there beingat least two silicon-bonded hydrogen atoms per molecule; and

iii. a platinum catalyst effective to cause copolymerization of (i) and(ii); and

b. thereafter drying the treated material.

The compounds of Formula (VI) may be linear, cyclic or resinous innature, but preferably is linear or resinous. One illustrative materialis a linear dimethyl hydrogen chain-stopped dimethylpolysiloxanematerial containing from 2 to 3 silicon atoms in the molecule. A furtherspecific compound may be a resinous copolymer of dimethylsiloxane units,methylhydrogensiloxane units and trimethylsiloxane units which containfrom 2 to 5 or 10 or more silicon atoms per molecule. Also illustrativeare 1,3,5,7-tetramethylcyclotetrasiloxane; a copolymer containing thethree dimethylhydrogen siloxane units and one monomethylsiloxane unitper molecule; and a low viscosity fluid composed ofdimethylhydrogensiloxane units and SiO₂ units in the ratio of 2 moles ofthe former to 1 mole of the latter. Especially useful is a linearmethylhydrogenpolysiloxane fluid or resinous methylhydrogenpolysiloxane.Such components are well known to those skilled in this art and aredescribed in U.S. Pat. No. 3,436,366, which is hereby incorporated byreference. Also. U.S. Pat. No. 2,491,843 describes a useful family oflinear trimethysilyl chain-stopped polysiloxanes. One is made bycohydrolyzing 5 parts of (CH₃ )₃ -- SiCl and 95 parts of CH₃ HSiCl₂ ;viscosity 100 cps. at 25° C.

The platinum catalyst employed in the practice of this invention may beany of the well known platinum catalysts which are effective forcatalyzing the reaction between silicon-bonded hydrogen groups andsilicon-bonded vinyl groups. These materials include the various finelydivided elemental platinum catalysts, such as those described in Bailey,U.S. Pat. No. 2,970,510, the chloroplatinic acid catalysts described inSpeier, U.S. Pat. No. 2,823,218, the platinum-hydrocarbon complexesdescribed in Ashby, U.S. Pat. Nos. 3,159,601 and 3,139,662 as well asthe platinum alcoholate catalysts disclosed in Lamoreaux, U.S. Pat. No.3,200,972. Regardless of the particular platinum catalyst employed, thecatalyst is used in an amount sufficient to provide from about 10⁻ ³ to10⁻ ⁶ gram atoms of platinum per mole of silicon-bonded vinyl groups inthe composition. On another basis, a useful range of catalyst willprovide one platinum atom for each 100 to 1,000,000 silicon-bonded vinylgroups in the silanol chain-stopped polysiloxane of Formula (I).Especially preferred is the range of 5-50 parts per million of platinumbased on the weight of the silanol chain-stopped polysiloxane of Formula(I).

The preferred compositions for rendering flexible sheet materialsnon-adherent to surfaces which normally adhere thereto will comprise:

a. from 1 to 50% of the polysiloxane of Formula (I) or Formula (II);

b. from 0.01 to 5% of the organic hydrogen polysiloxane;

c. from 0.00001 to 0.0005% of platinum in the form of a salt or complex;and

d. from 60 to 98% of water.

The polysiloxane of Formula (I) is a novel polymer and it may beemployed in the emulsion without being isolated in substantially pureform. It may also be isolated according to the techniques employedhereinafter in Test A. This polymer may be combined with anorganohydrogensiloxane and cured into release or water-repellentcoatings for application to paper, cloth and other substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the process of the present invention.They are illustrative and the claims are not to be construed as limitedthereto.

EXAMPLE 1

To a stainless steel beaker, the following materials were added;

    ______________________________________                                        [(CH.sub.3).sub.2 SiO].sub.4                                                                       522.15    grams                                          [(CH.sub.3)CH.sub.2 CHSiO].sub.4                                                                   2.85      grams                                          Platinum catalyst*   0.40      grams                                          Distilled water      525.00    grams                                          Dodecylbenzene sulfonic acid                                                                       7.50      grams                                          ______________________________________                                         *Of the type described in Lamoreaux, U.S. 3,220,972.                     

These materials were agitated for 30 minutes and then homogenized at6500 psi through a Manton-Gaulin homogenizer. The emulsion was thenheated to 70° C. and held at 70°-75° C. for 3.0 hours. The heat wasremoved and the emulsion was allowed to cool for 4.0 hours. At the endof the 4.0 hours, 3.8 grams of triethanolamine was added to neutralizethe dodecylbenzenesulfonic acid and agitation was continued for 1.0hour.

The resulting emulsion had a solids content of 43.7%. The emulsionviscosity was 350 cps. In order to determine the extent of thepolymerization reaction, a portion of the siloxane fluid was recoveredfrom the emulsion after using isopropyl alcohol to break the emulsion.The fluid was dried at 150° C. for 3-4 hours to remove residual alcoholand water. This fluid was found to have a viscosity of about 248,000centipoises. Since the drying process undoubtedly removed some siloxanelight ends, the values obtained for the viscosity of the siloxane fluidis probably higher than the "true" viscosity.

EXAMPLE 2

To a stainless steel beaker, the following materials were added:

    ______________________________________                                        [(CH.sub.3).sub.2 SiO].sub.4                                                                       855.2     grams                                          [(CH.sub.3)CH.sub.2 CHSiO].sub.4                                                                   4.5       grams                                          Platinum catalyst*   0.60      grams                                          Distilled water      1118.8    grams                                          Dodecylbenzene sulfonic acid                                                                       12.4      grams                                          ______________________________________                                         *Same as Example 1.                                                      

The homogenization and heating cycle were carried out as in Example 1.At the end of the 3.0 hours heating cycle, the emulsion was split intotwo parts. Part A was cooled for 3.0 hours at ambient temperature beforeneutralization while Part B was cooled for 5.0 hours beforeneutralization. The physical properties of both products were evaluatedand found to be as follows:

    ______________________________________                                                      Part A    Part B                                                ______________________________________                                        % solids        38.8%       39.9%                                             Emulsion viscosity                                                                            76 cps.     93 cps.                                           Fluid viscosity*                                                                              168,000 cps.                                                                              320,000 cps.                                      ______________________________________                                         *Determined in the same manner as in Example 1.                          

TEST A

To demonstrate the stability of the emulsion produced by the process ofthe invention, the following procedures were carried out using thematerial produced in Example 1.

a. Freeze-Thaw Stability--20 grams of the polysiloxane compositionprepared in Example 1 was frozen at 15° C. daily for 4-6 hours and thenallowed to thaw at room temperature. Testing was discontinued after 14such cycles. There was no separation of free oil or any other apparentdamage to the emulsion.

b. Emulsion and Dilution Stability--The emulsion of Example 1 wassubjected to a standard test designed to determine the stability anddilution stability of different silicone emulsions. A sample of theemulsion was placed in a specially designed centrifuge tube andcentrifuged for 80 minutes at 500 RPM's. After centifuging, samples wereremoved from the top and bottom layers of the emulsion and the percentsolids were determined. The gradient for any particular emulsion isdefined as:

    Straight Gradient = (% solids of top layer) - (% solids of bottom layer) = T.sub.4 -B.sub.1

the lower the value of the gradient, the more stable is the particularemulsion. Note: This is an accelerated test which is useful indetermining the "shelf life" of an emulsion.

In a similar manner, a dilute gradient is determined. In this case, 1.0part of emulsion is diluted with 9.0 parts of water and agitated brieflyto ensure uniformity. This diluted sample is then centrifuged as aboveand samples taken for percent solids determination. In the dilutegradient test, the gradient is defined as: ##EQU1##

Silicone emulsions prepared by conventional emulsification normally givestraight gradient values (T₄ -B₁) of from 2.0 to 5.0 and dilute gradientvalues (T₄ /B₁) of 1.5 to 3.0.

When the emulsion of Example 1 was subjected to the test as describedabove, the straight gradient value was -0.18 and the dilute gradientvalue was 1.01. These results indicate that the emulsions of thisinvention are much more stable than silicone emulsions prepared byconventional emulsification techniques.

In a separate test, 15 grams of the composition produced in Example 1was diluted with 135 grams of water and agitated in a Waring blender for1.0 hours at approximately 10,000 RPMs. After agitation, there was noseparation of free oil.

EXAMPLE 3

The sample of material that was subjected to the Freeze-Thaw procedureof Test A was formulated into the following coating bath:

    ______________________________________                                        Polysiloxane emulsion of Example 1                                                                  10.30     grams                                         Methylhydrogen-containing                                                     siloxane and vinyl chain-stopped                                              siloxane (40% emulsion)*                                                                            0.60      grams                                         Dispersant**          0.25      grams                                         Water                 38.85     grams                                         ______________________________________                                         *Emulsion 3, Serial No. 419,372                                               **Natrolsol 250 HR, a non-ionic water soluble hydroxyethyl cellulose.    

This bath was coated onto a Plainwell semibleached kraft paper using aNo. 5 Meyer rod and cured for 30 seconds at 300° F. Complete cure wasachieved in this time, there being no smear, no migration and norub-off. A sample of this coated paper was laminated to Johnson andJohnson adhesive tape and aged for 20 hours at 70° C. After aging, therelease value was checked. Release was 35 gms./in. at 12 in./min.

EXAMPLE 4

A polysiloxane composition was prepared according to the method ofExample 2 and formulated into the following coating bath:

    ______________________________________                                        Polysiloxane emulsion of Example 2                                                                  9.7       grams                                         Methylhydrogen-containing                                                     siloxane and vinyl chain-stopped                                              siloxane (40% emulsion)                                                                             0.6       grams                                         Dispersant*           1.0       grams                                         Water                 38.7      grams                                         ______________________________________                                         *PVA-Elvanol 72-60, a polyvinyl alcohol (98% hydrolyzed).                

This bath was coated onto a Plainwell semibleached kraft paper as inExample 3. A 3 mil thickness of a water based SBR adhesive was appliedto the coated paper and then dried 3 minutes at 300° F. After drying,the coated paper was laminated to vinyl film. Samples were checked forinitial and aged release.

    ______________________________________                                        Average values (gms./in. at 12 in./min.)                                      Initial 5 Day at 140° F.                                                                      2 Weeks at 140° F.                              ______________________________________                                        100     40             38                                                     ______________________________________                                    

EXAMPLE 5

A polysiloxane was prepared by a procedure similar to that employed inExample 2 (Part B) and a bath was formulated as follows:

    ______________________________________                                        Polysiloxane emulsion 11.80     grams                                         Methylhydrogen-containing                                                     siloxane and vinyl chain-stopped                                              siloxane (40% emulsion)                                                                             0.60      grams                                         Dispersant*           0.25      grams                                         Water                 37.75     grams                                         ______________________________________                                         *Natrosol 250 HR                                                         

This formulation was tested according to the procedure set forth inExample 4, except that cure conditions were varied as outlined below.Both initial and aged release values were determined.

    ______________________________________                                                Release values (gms./in. at 12 in./min.)                              Cure Time           1 Week      2 Weeks                                       at 300° F.                                                                       Initial   at 70° C.                                                                          at 70° C.                              ______________________________________                                        20 sec.   40        23          20                                            30 sec.   33        28          23                                             30 sec.* 30        20          18                                            ______________________________________                                         *Sample not coated until the coating bath had been aged for 5 hours at        25° C.                                                            

EXAMPLE 6

At various times the cure characteristics of samples prepared in amanner similar to those of Examples 1 and 2 were compared to samples ofemulsion prepared according to procedures set forth in copendingapplication Ser. No. 419,372, filed Nov. 27, 1973, now U.S. Pat. No.3,900,617 e.g., Example 1 of that application.

It was found in a series of tests that emulsion baths prepared asdisclosed in this application would exhibit complete, migration-freecure after 30 seconds at 300° F., while samples of material prepared inthe conventional manner still showed incomplete cure (migration) evenafter 45-60 seconds at 300° F. This difference was specific to certainsubstrates such as Hudson clay coated draft paper (with a latex-proteinbinder) and Brown Co.'s natural colored parchment.

EXAMPLE 7

To a stainless steel beaker, the following materials were added:

    ______________________________________                                        [(CH.sub.3).sub.2 SiO].sub.4                                                                        350.0     grams                                          ##STR4##              0.45      grams                                        Distilled water       643       grams                                         Dodecylbenzene sulfonic acid                                                                        5.0       grams                                         ______________________________________                                    

The homogenization procedure and heating cycle were carried out in thesame manner as previous Examples. The cooling cycle was carried out for8.0 hours before the addition of 2.5 grams triethanolamine. Theresulting emulsion had a percent solids of 31.9% and an emulsionviscosity of 18.5 cps. The fluid made by this process had a viscosity of43,000 cps.

EXAMPLE 8

To stainless steel beaker, the following materials were added:

    ______________________________________                                        [(CH.sub.3).sub.2 SiO].sub.4                                                                        522        grams                                        [(CH.sub.3)CH.sub.2 CHSiO].sub.4                                                                    2.85       grams                                         ##STR5##              As required (less than 0.05% by weight)                Distilled water       525        grams                                        Dodecylbenzene sulfonic acid                                                                        7.50       grams                                        ______________________________________                                    

Following the same processing procedures as given in previous Examples,would yield an emulsion of physical properties comparable to those givenin previous Examples.

In this particular case, the viscosity of the siloxane may be controllednot only by the length of the cooling cycle, but also by the amount oftrimethylsilyl chain-stopper. The smaller the amount of this source oftrimethylsilyl chain-stopper, the higher the polymer viscosity.

Obviously, many variations will suggest themselves to those skilled inthe art from the above detailed description without departing from thescope or spirit of the invention. It is, therefore, to be understoodthat changes may be made in the particular embodiments of the inventiondescribed which are within the full intended scope of the invention asdefined by the appended claims.

I claim:
 1. A process for rendering flexible sheet material non-adherentto surfaces which normally adhere thereto which process consistsessentially of:a. treating the sheet material with an aqueous emulsioncontaining:i. a neutralized polysiloxane emulsion produced by theprocess comprising:1. homogenizing a mixture which consists essentiallyof:A. a compound of the formula (R₂ SiO)₄ wherein R is a monovalenthydrocarbon free of unsaturation; B. a compound of the formula:

    (RR.sup.1 SiO).sub.4

wherein R is the same as hereinabove defined and R¹ is a hydrocarbonradical having vinyl unsaturation; and C. a benzene sulfonic acidcompound of the formula: ##STR6## wherein R² is an alkyl group of from6-18 carbon atoms and; D. water;
 2. 2. heating the homogenized mixtureof (1) to form said polysiloxane; and3. adding a neutralizing amount ofan alkanolamine to said mixture to neutralize said benzene sulfonic acidand to form a neutralized emulsion of said polysiloxane, saidpolysiloxane having the formula: ##STR7## wherein R is a monovalenthydrocarbon radical free of unsaturation; R¹ is a hydrocarbon radicalhaving vinyl unsaturation; x and y are positive integers so that thesilanol stopped polysiloxane has from 0.1 to 1% by weight of R¹ groupsand the viscosity of the polymer ranges between 25,000 centipoises and1,000,000 centipoises; ii. an organic hydrogen polysiloxane having theformula:

    (R).sub.a (H).sub.b SiO.sub.(4.sub.-a.sub.-b)/2

wherein R is a monovalent hydrocarbon radical free of unsaturation; a isfrom 0 to 3; b is from 0.005 to 2.0 and the sum of a plus b is fromabout 0.9 to 3, there being at least two silicon-bonded hydrogen atomsper molecule; and iii. a platinum catalyst effective to causecopolymerization of (i) (ii); and b. thereafter drying the treatedmaterial.
 2. The process of claim 1 wherein said polysiloxane has theformula: ##STR8##
 3. The process of claim 1 wherein the platinumcatalyst is included in the homogenized mixture of step (1).
 4. Theprocess of claim 1 wherein the heating step (2) comprises heating thehomogenized mixture at a temperature of from 40°-100°.
 5. The process ofclaim 1 wherein heating step (2) is followed by a cooling step.
 6. Theprocess of claim 5 wherein the benzene sulfonic acid isdodecylbenzenesulfonic acid.
 7. The process of claim 6 wherein thealkanolamine is selected from compounds of the formula;

    (R.sup.3 OH).sub.3 N

wherein R³ is lower alkylene of from 1 to 8 carbon atoms.
 8. A processas defined in claim 3 wherein the platinum catalyst is present in anamount to provide one platinum atom per 100 to 1,000,000 silicon-bondedvinyl groups in the poly-organosiloxane component.
 9. A process asdefined in claim 1 wherein the aqueous emulsion comprises:i. from 1 to50% of the polysiloxane; ii. from 0.01 to 5% of the organic hydrogenpolysiloxane; iii. from 0.00001 to 0.0005% of platinum in the form of asalt or complex; and iv. from 60 to 98% of water.